Optical links are widely used to move data between devices in a communications network. In comparison with electrical links, optical links have greater range and can transport more data per unit of physical media. Although network devices capable of all-optical operation are known, it is more typical that the receiving device performs signal processing in the digital electrical domain. It is therefore necessary to convert the received optical signal to a digital electrical signal at the receiving device so that processing may be done.
Circuits for converting signals from the optical domain to the digital electrical domain are known. As shown in FIG. 1, a continuous-time front end includes a PIN diode (100), a discrete, low noise transimpedence pre-amp (102) and Automatic Gain Control (“AGC”) amplifier (104) connected with an array of Analog to Digital Converter (“ADC”) circuits (1061-106n). The PIN diode is used to convert the incoming optical signal to an electrical signal. The low noise trans-impedance pre-amplifier and AGC amplifier are used to provide analog signal conditioning, such as the requisite voltage level and current to drive time-interleaved ADCs. The ADCs are time-interleaved in order to permit an effectively lower clock rate in each individual ADC circuit relative to the optical signal. Track-and-hold or possibly sample-and-hold circuits (shown as transistor switches in FIG. 1) are employed to select individual ADC circuits. In particular, the ADCs are selected in round-robin such that only one ADC circuit is selected at a given point in time. However, continuous time front ends have some drawbacks. In particular, they have limited dynamic range and require frequency response equalization. Discrete pre-amps and AGCs also require space, dissipate power and are relatively costly. Further, interconnecting the discrete elements in a manner that provides adequate bandwidth can be difficult, and it seems impractical to integrate a conventional pre-amp and AGC into a CMOS chip that is also capable of the required ADC and Digital Signal Processing (“DSP”) functions.